The invention relates to a steam trough mangle, which can also be referred to as a hot bed ironer, for drying and smoothing damp pieces of laundry, the contact surfaces of which are heated by means of a flowable heat carrier medium in the form of live steam.
Recently, the problem of saving energy and of optimizing the use of energy in technical processes has become increasingly more acute. This has especially affected the energy-intensive process of drying textiles, such as pieces of laundry, as it is carried out in steam-trough mangles for instance. The goal is to reduce the specific energy requirement for drying a piece of laundry. One way, among others, of achieving this aim is the pre-drying of such pieces of laundry before the calendering process itself.
Trough mangles are already known, in which pre-heating and pre-drying of the laundry pieces to be dried takes place by means of contact with a heated surface, before the calendering process itself is carried out (DE-Gm No. 1,789,610; 8 d; 20/04). The laundry is passed over a heated external surface of the trough mangle. Herein, however, the cold, damp laundry must slide on the heated contact surface. The thermal energy required for the pre-heating and pre-drying is withdrawn from the mangle, i.e., it needs to be additionally expended. Furthermore, this principle can be applied only with difficulty to multiple-trough mangles.
For this reason, it has already been proposed to use the condensate obtained from the heating of the trough mangles and the trough-bridges to heat a rotatably mounted and drivable pre-drying cylinder, arranged in front of a mangle unit, comprising a mangle cylinder and a trough-mangle that at least partially encircles the mangle cylinder on its jacket side, wherein, for the purpose of pre-drying of the laundry pieces, the latter are guided in such a way that they bear against the external wall of the pre-drying cylinder and partially rotate with such cylinder (DE Patent Application No. P 30 41 244.3).
For this purpose, the condensate is collected in a vessel, and guided from there by means of a pump, to channels arranged on the internal side of the hollow pre-drying cylinder and extending between the front ends thereof. Supply of the condensate to these channels is carried out at the front end of the pre-drying cylinder, while withdrawing is effected at the opposite end.
However, since the condensate is under high pressure, the depressurization which necessarily originates at the suctioning end of the pump by reason of the cavitation effect will lead to destruction of the pump.
Furthermore, with such an arrangement of the channels, sufficient uniform heat transfer to the surface of the pre-drying cylinder across its width cannot be achieved.
In order to obtain a satisfactory pre-heating or pre-drying of the laundry pieces, further guiding elements have been arranged in the area of the pre-drying cylinder, which the laundry pieces need to contact. Such guiding elements are heated with live steam, thus additional thermal energy is required. However, the desire to save energy in the steam-trough mangle is thereby not taken into account.
It is the object of the invention to improve the energy balance of the steam trough mangle.